RC224ATL/224ATLV
6.0 Operation
EmbeddedModem Family
6.5 Call Progress
6.5.2 Ring Detection
Ring detection is based on a digital input to the modem. External circuitry not
part of the modem is required to convert the analog 40 to 150 V
ring signal to
RMS
a digital single-bit data stream representation. Valid ring frequencies of 15.3 to 68
Hz are detected. Detection is achieved by counting valid high to low ring signal
transitions. Valid transitions consist of a high state of 2 to 34 ms followed by a low
state of 2 to 42 ms. Ring signals that have transition counts less than the nominal
value are discarded.
In addition to valid high to low transitions, ring detection depends on the
cadence of the ring ON time (valid transitions occurring) and ring OFF time (no
valid transitions). Ring OFF times must be greater than 0.5 seconds. Ring ON
times must be greater than 125 ms at 20 Hz (100 ms at 68 Hz).
Ring detection is integrated over 8 seconds. All counters and timers are reset
at 8 second intervals. The modem will answer the ring after N valid ON/OFF ring
cycles. N is programmable via the S0 register. Upon detecting N rings, the
modem verifies that the current ring state has been in the OFF state for 0.5
seconds before seizing the line.
Table 6-5 lists the Fax Class 1 calling sequence; Table 6-6 lists the answering
sequence.
Table 6-5. Fax Class 1 Calling Sequence (1 of 2)
DTE Commands
(Host)
DCE Responses
(Modem)
Remote Fax
Notes
(1) AT+FCLASS=1
(2) OK
—
Set to Class 1
PHASE A
(3) ATDT6163
(4) Dials
(6) CONNECT
(5) Answers
(7) Send HDLC flags
+FRH=3 implied by Dialing
PHASE B
—
—
(8) Send NSF frame
—
—
(9) <NSF>, OK
(11) CONNECT
—
—
—
(10) AT+FRH=3
—
—
—
(12) Send CSI frame
—
—
(13) <CIS>, OK
(15) CONNECT
—
—
—
(14) AT+FRH=3
—
(16) Send DIS frame
(18) Drop carrier
(21) Receive flags
—
—
—
Last frame bit = 1
—
(19) AT+FTH=3
—
(17) <DIS>, OK
(20) Send HDLC flags
(21) CONNECT
(23) Send TSI frame
(25) CONNECT
(27) Send DCS frame
(29) Detect last frame bit
—
—
—
(22) <TSI>
—
(24) Receive TSI
—
Last frame bit = 0
—
Last frame bit = 1
—
(26) <DCS>
—
(28) Received DCS
—
D224ATLVDSC
Conexant
6-13
CONEXANT [ CONEXANT SYSTEMS, INC ]
